Rail flaw detector mechanism



Dec. 26, 1950 H. c. DRAKE El'A L 2,535,353

RAIL FLAW DETECTOR MECHANISM Filed Saiat. 29, 1949 6 Sheets-Sheet 1 FIG! l l .I/ l I 19 12 30 27 22 2! 2a 20 40 ll 19 33 32 HARCOURT C. DRAKE WALDEIAR 1. BENDZ WILLIAM E. MESH ATTORNEY.

Dec. 26, 1950 H. c. DRAKE ETAL 2,535,353

RAIL FLAW DETECTOR MECHANISM Filed Sept. 29, 1949 6 Sheets-Sheet 2 mm mm Q 9 Qh 9n um N OE INVENTORS. HA'RCOURT C. DRAKE WALDEHAR I. BENDZ WILLIAM E. MESH B 1% ATTORNEY Dec. 26, 1950 H. c. DRAKE? ETAL 2,535,353

RAIL FLAW ns'rsc'ron MECHANISM Filed Sept. 29, 1949 s snows-sheet s aid! W".. I h I\ l1.

INVENTORS. HARCOURT C. DRAKE WALDENAR I. BENDZ WILLIAM E. MESH Dec. 26, 1950 H. c. DRAKE ETAL 2,535,353

RAIL FLAW DETECTOR MECHANISM Filed Sept. 29, 1949 6 Sheets-Sheet 4 F'IG.4

INVENTORS. HARCOURT c. DRAKE wALoEuAR 1. asnoz WILLIAM E. MESH w WM M ATTORNEY.

H. C. DRAKE EI'AL RAIL FLA DETECTOR MECHANISM 6 Sheets-Sheet 5 INVENTORS.

an A Y. R E F O R ua m HANK W M CM L L E mu Filed Sept. 29, 1949 mm mm 6 Sheets-Sheet 6 H C. DRAKE ET'AL RAIL FLAI DETECTOR IIECHANISII Dec. 26, 1950 Filed Sept. 29, 1949 INVENTORS. HARCOURT C. DRAKE LDEMR I. BENDZ WILLIAM E. \ESH BY XX ATTOR'EY.

Patented Dec. 26, 1950 UNITED STATES PATENT OFFICE RAIL FLAW DETECTOR MECHANISM York Application September 29, 1949, Serial No. 118,562

21 Claims.

This invention relates to rail flaw detector mechanisms and is particularly designed for application upon the type of mechanism employed on the Sperry rail fiaw detector car. This car operates upon the principle of energizing the rail with fiux, as, for instance, by passing current through the rail to establish an electromagnetic field surrounding the same and exploring said field by inductive means to discover any irregularities caused by the presence of fissures or other discontinuities in the rail. The particular problem which presents itself here arises from the fact that rails are joined by angle bars, bolts, etc., which joints constitute in themselves irregularities in the rail which will cause variations in the fiux in the same manner as an internal fissure. Therefore, as the detector car rides along the rail, the detector mechanism in passing over a rail joint gives rise to a large number of closely bunched indications on a recording tape, which indications are not distinguishable from one another nor from the indications which may be caused by an internal defect in the rail. It has therefore been the practice to provide cutout means which would cut out the indicating mechanism for a predetermined distance in advance of and after leaving the angle bar so as to prevent actuation of the indicating means throughout the entire region where the electromagnetic flux could be distorted by the angle bar. Such mechanism has heretofore taken the form of either mechanical means such as pivoted fingers designed to engage the angle bar or electric means such as potential contacts which on engagement with the ends of the rail actuated electrical cutout means for cutting out the indicating mechanism.

It is the principal object of this invention to provide cutout means which may be controlled by a magnetic recorder which may take the form of a continuous member comprising magnetic material, such as an endless magnetic tape or wire, or a disc.

It is a further object of this invention to provide a cutout means which maintains fixed relationship to the distance traversed by the car.

It is another object of this invention to provide cutout means of the type described which may be adjusted for various lengths of angle bars.

Further objects and advantages of this invention will become apparent in the following detailed description thereof.

In the accompanying drawings,

Fig. l is a side elevation of a portion of a rail fissure detector car having the invention applied thereto.

Fig. 2 is a diagrammatic representation of one embodiment of the invention.

Fig. 2A is a view similar to a portion of Fig. 2, showing another form of the invention.

Fig. 3 is a detail wiring diagram of the Fig. 2 form of the invention.

Fig. 4 is a view similar to Fig. 2 showing another form of the invention.

Fig. 5 is a detail wiring diagram of the Fig. 4 form of the invention.

Fig. 6 is a view similar to Fig. 2 showing still another form of the invention.

Fig. '7 is a detail wiring diagram of the Fig. 6 form of the invention.

Referring to Fig. 1 of the drawings, there are shown parts of a standard Sperry rail fissure detector car which includes a car body I0 operating along the rails R. Fissure detection is accomplished by energizing the rail with flux by passing a current through each. rail from a generator G within the car body, supplying current to spaced current brushes H and I2 supported upon the current brush carriage i3 which when in lowered or effective position is adapted to ride upon the rail by means such as wheels IS. The current brush carriage i3 is normally held in elevated or ineffective position by means of springs, not shown, and cables it, but when it is desired to lower said carriage, fluid pressure such as compressed air is supplied to the cylinders IT to force out piston rods is which are pivotally connected at l9 to the current brush carriage ii. The current passed through the rail by way of spaced brushes H and i2 will establish an electromagnetic field surrounding the rail and this field will be uniform except in the region of fiaw where it will be distorted. Such distortions of the electromagnetic field are detected by a fiaw responsive mechanism which may take the form of a plurality of pairs of opposed induction coils 20, 2|, 22 supported in a housing 23 at a constant distance above the rail surface by means of a carriage 24. Said carriage 24 is mounted on current brush carriage 13 by means of loosely fitting bolts 25 and springs 26 to permit said carriage 24 while riding on the rail on means such as wheels 21 to move independently of carriage I! so that the said carriage 24 may at all times maintain parallelism with the rail surface regardless oi irregularities thereof. The sets of coils 20, 2 l, 22 normally cut the same number of lines of force but on entering a region of flaw, first one coil of each pair and then the other will cut a different number of lines of force to generate a differential E. M. F. which after being suitably amplifled by amplifiers such as amplifiers A,

accuses A, A" may be caused to actuate recording apparatus such as pens P operating on a chart 0. At the same time that the pens are actuated there is actuated also marking means which may take the form of a paint gun 30 mounted on the current brush carriage I! a sumcient distance behind the fiaw responsive members 20, 2!, 22 to compensate for the movement of the car and for the lag in operation of the paint gun.

As stated in the introduction hereto the joints which hold the rails together comprise angle bars 32, bolts 32 and additional members, all of which serve to deflect the current passing through the rails and vary the electromagnetic field surrounding the same. The irregularities of the angle bar will cause the detector coils to pick up a large number of variations in the electromagnetic field and this in turn will cause the pens to record upon the chart a large number of closely bunched indications. Since the current deflection caused by the angle bar commences a considerable distance in advance of the bar and extends its influence for a similar distance beyond the leaving end of the bar. it will be understood that there is a considerable portion of the rail within which a will be difllcult to discover any internal defect because any indication of variation in fiux caused by the internal defect will be merged with and be indistinguishable from the large number of indications set up by the angle bar within the region ailfected thereby. It is therefore the practice to provide means for cutting out the indicating means throughout the region of electromagnetic flux affected by the angle bar.

To accomplish the above result there is provided the following mechanism: In advance of the detector housing 23 which supports the detector coils there is provided a pair of joint trip contacts 40 spaced along the rail and which normally measure the potential drop along the rail. The meeting edge of two rails will provide an extraordinarily large potential drop which is applied through an impedance matching transformer T to amplifier tube 35 whose output triggers a thyratron tube 36 which then rapidly energizes a magnetizing or impressor coil 31 of a magnetic recording mechanism. This pulse transmitted by the joint trip amplifier when the com tacts 40 pass over the ends of the rails will be impressed by coil 31 on a continuous member comprising magnetic material, such as an endless magnetic wire or tape 42. as shown in Fig. 2 or the periphery of a disc 42' as shown in Fig. 2A. When a wire or tape 42 is used, it passes over pulleys 44 and 45, the latter being driven by belt 45 from the car axle 41 through suitable gearing. Contacts 40 are positioned sufilciently in advance of the housing 23 so that they will engage the rail ends when the first set of coils 20 is a predetermined distance from the region afifected by a joint. Therefore after traveling a predetermined length of rail after contacts 40 engage the rail end, the first pair of coils 20 will reach the region aflected by the angle bar and therefore will require that the amplifier A which amplifies the output of coils 20 be rendered ineffective to actuate the indicating mechanism. The record impressed by impressor coil 31 on tape 42 in response to the voltage drop across the rail ends will reach a receiver or reproducer pick-up coil 50 after the herelnbefore mentioned predetermined distance has been traversed by coils 2. after contacts 40 engage the rail end.

When coils 20 reach the region of flux ailected by the joint the pulse which has been impressed by coil 31 on tape 42 reaches coil 50 which should then operate a turn-o! circuit to render the indicator ineffective to be operated by the output of amplifier A in response to pulses generated by coils 20. As soon as coils 20 leave the region of flux affected by the angle bar, the pulse impressed by coil 21 on tape 42 reaches coil 80 which should then operate a turn-on circuit to render the turn-oi! circuit ineffective and the indicator again efiective. Since the member 42 is continuous, the pulse impressed by coil 31 is erased by.

erasing coil 8| energized by a suitable source of A. C. in advance of impressor coil 31.

Where the periphery of a disc 42 is employed as the continuous member, the periphery is supplied with magnetizable material and the coils ll, 31, 50, 50', 50", B0, B0 and 60 are positioned around the periphery. The disc is driven from axle 4'! in the same manner as the tape or wire.

The details of one practical embodiment for accomplishing the above described functions are disclosed in Fig. 3. In the manner previously described, as a magnetized section of tape 42 passes under the first turn-oil coil 50 a rise in 4 potential across terminals 5| and 5| is experienced. This change in potential maybe amplified by any suitable amplifier 52 whose output is connected to a thyratron tube 53. The. anode circuit of tube 53 consists of a suitable source of D. C. potential. illustrated as battery 54 and resistors 55 and 55. The resistor 55 is connected to the grid control circuit of tube 51 which may be the final stage of amplification of amplifier A whoseoutput actuates a relay 58 to attract its armature which may be a pen P operated on the traveling chart C. Thus if tube 51 is rendered non-conducting, the indicating apparatus is likewise rendered inoperative. In the system described, a change in potential across turn-off coil 50 in response to the pulse impressed on tape 42 by coil 31 instantly results in conduction of thyratron tube 53 causing a rise in potential across resistor 55 with the polarity indicated in Fig. 3. The potential across resistor 55 instantly produces a high negative voltage at the grid of final amplifier tube 51 thereby biasing it beyond cutofl' and rendering it non-conducting. In this manner the recording apparatus is turned off by the action of thyratron tube 53.

The indicaing or recording mechanism actuated by the output of amplifier A should remain inefiectlve until the coils 20 have passed beyond the region of flux affected by the rail joint. This distance corresponds to the movement of a point on the tape from coil 50 to coil 60. When the pulse impressed by coil 31 reaches coil 60 the indicating mechanism actuated b the output of amplifier A should be rendered again eil'ective. For this purpose the coil 60 actuates turn-on mechanism as follows: Coil 60 is connected to amplifier 5| so that the output of the amplifier fires a thyratron tube 62. The anode circuit of tube 52 consists of a source of D. C. potential which may be battery 63 and resistors 56 and 64. The anode circuit may also include the normally closed contacts 65 of a relay 66. When tube 52 conducts, the poential across resistor 64 instantly develops with the polarity indicated in Fig. 3. Proportions of the circuit constants are made such that the potential thus manifest across resister 54 as tube 82 becomes conducting is approximately equal to the potential across resistors 55 and 58 combined when tube 53 is conducting. {Because of this circuit condition the potential at the anode of tube It is approximately zero or negative when tube 02 conducts. Thus tube II is immediately extinguished by the firing of tube.

2. The previousl established potential across resistor I! immediately reduces to zero and the function of the final amplifier tube 51 is re-established to render the indicating mechanism again effective.

When the turn-on tube 82 fires, the rise in potential across resistor 64 begins to charge capacitor 61 through resistor 08 with the polarity illustrated in Fig. 3, but with the action delayed because of the series connection of resistor 88 and capacitor 1. Reset timer tube 89 is normally biased non-conducting by means of bias potential II. The slowly rising voltage across capacitor 81 opposes bias voltage ll so as to permit tube 09 eventually to become conducting. When this condition is satisfied, anode current of tube 69 energizes coils 06 to open contacts 85. This interrupts the anode circuit and flow of current through tube 62. Thus the turn-on tube 62 is reset and the circuit made in readiness for the next signal. ?otential across resistor 84 disappears and the circuits of relay timer tube 89 are also reset. It is to be noted that this latter function of timer tube 88 does not bear upon the accuracy of operating either the turn-oil or turn-on circuits. Hence, accuracy of the circuits performing the objective of this invention does not depend on the function of timer tube 89.

It will be understood that each pair of coils 20, 2!, 22 will be rendered ineffective to actuate its recording mechanism when it reaches the region of iiux affected by the joint and will be rendered again effective to actuate its recording mechanism when it has passed beyond the region of flux. affected b the joint. Thus just as coils iill and 60 are positioned to represent the turn-on and turn-off points for coil 20, so coils 50' and 60' are positioned along the tape to represent the turn-oi! and turn-on points of coil 2i and coils iii)" and 60" represent the turn-off and turn-on points for the coils 22. Just as the turmoil and turn-on circuits controlled by coils B and 60 affeet the amplifier A preferably by rendering the last stage amplifying tube ineffective, so coils 50 and 60' act upon the last stage tube of ampliher A and coils 80" and 80" act upon the last stage tube of amplifier A" through turn-of! and turn-on circuits similar to those described.

It is necessary to provide an adjustment for the distance between the Joint trip contacts 50 and the leading pair of coils which distance determines the point at which the cu -out is to begin. This point is usually the point where the rail Joint begins seriously to affect the flux surroundingthe rail. In order to make this adjustment, the coils til, 50' and 50" may be actuated as a unit (since their relative positioning is fixed) toward or away from coil I? which corresponds to the position of contacts 40, by any suitable adjusting device shown diagrammaticall as a knurled knob i! which actuates a threaded screw 76 into and out of a suitable support 11 which supports the three coils. Thus the cut-oi! point for the recording apparatus may be varied so that the coils 20, 2i, 22 may test closer to or further from the ang e bar before th recording mechanism is cut out.

A second adjustment is necessary for the length of rail which is cut out. This length is as stated in the introduction hereto usually the length of the angle bar and a predetermined distance at either end of the bar. This cut-out distanc is represented by the distance between coils II. IO, II" and coils ill, ll, OI" respectively. Therefore, once the coils IO, 50' and II" have been adjusted with respect to impressor coil I! which represents the position of the contacts 40 at the Joint, the coils 80, 60' and 60" may be adjusted as a unit with respect to the coils 50, II, N". For this purpose an adjusting mechanism ll, 10', 11' may be utilized, this mechanism being shown diagrammatcally and being similar to adjusting mechanism 18, 16, 11.

A modified form of the invention is disclosed in Fig. 4 in which a different method is employed for rendering ineffective and effective the recording mechanism controlled by each pair of coils. In this form of the invention instead of the thyratron discharge type of control disclosed in Fig. 3, there is employed a flip-flop circuit which is actuated in one direction for rendering the recording apparatus ineffective and in the opposite direction for rendering the recording apparatus again effective. In this form, as disclosed in Fig. 4 in which similar parts to those in Fig. 2 bear similar numbers, there is again disclosed the impressor coil 31 actuated by the joint trip contacts 40 and there are again employed a plurality of coils 50, 50 whose position relative to coil 31 corresponds to the positioning of coils 26 and N relative to contacts 40. Furthermore, there are shown coils 60, fill whose positioning relative to coils 50, 50' represents the length of rail whose flux variations are not to be recorded. Only two coils 50, 50' and Gil, 60' are shown, for the pur-- pose of illustrating the invention, corresponding to coils 20 and 2!, but as many cells similar to t ll, 60 and 50, 60 may be employed as there are sets of detector coils. Whereas in Fig. 2 coil 50 actuated a gas discharge tube circuit to render the recorder ineffective and another gas discharge tube to render the recorder apparatus again effective, in this form of the invention coil for example, actuates a flip-flop circuit 80 which is actuated in one direction by coil 50 to render the recording mechanism controlled thereby ineffective, and is operated in the opposite direction by coil 60 to render the recording mechanism again effective. Similarly, coils 50 and 60 actuate a second flap-flop circuit at to render the recording mechanism controlled thereby ineffective and effective. The specific circuit for accomplishing this result may be as dis closed in Fig. 5.

Fig. 5 shows one well-known type of flip-flop circuit 86 wh'ch may accomplish the abovedescribed result. The pulse impressed on the tape H by coil 31 generates a. voltage in coil 50 when that magnetized portion of the tape passes beneath coil 50.

Assume that the left-hand tube is conducting. The circuit is designed so that only one tube at a time can conduct. A negative pulse from co'l 59 is applied to the grid of tube 85. This lowers the grid voltage to a point below cut-off, quenching tube 85. The anode voltage of tube 85 rises toward the B+ voltage. This rise is translated in the circuit to a rise in grid voltage of the right-hand tube 81 to a point above cut-off which allows the tube 81 to conduct. In conducting, the anode voltage of tube 81 drops, lowering the gr d voltage of tube 85 to a point below cut-oil. Drop in the anode voltage of tube 81 is used to desensitize the amplifier tube 51 by lowering the screen voltage.

It will be understood that the same adjustments of position of coils 50, 50', etc., relative to coil 31 assasss 7 and of coils ill, I, etc., relative to coils II, II, etc., may be made as in Fig. 2.

Still another form of this invention is disclosed in Fig. 6. In this form the engagement of the joint trip contacts 40 with the rail joint causes two coils 31 and 31' to impress two magnetic impressions on the tape 2 simultaneously. The position of coil 31' with respect to coil 81 may be adjusted by any suitable adjustment shown diagrammatically at 88, 89, 90 similar to adjustment II, 16, 11, so that the distance oi 31' from 31 corresponds to the region of fiux affected by the rail joint. The flip-flop circuit which is controlled by the impressions on the tape, instead of being actuated by two spaced pick-up coils such as 50. 60, is actuated by a single coil 8| which successively picks up the spaced impressions made by coils 31 and 31'. Thus when the impression made by coil 31 passes beneath coil 9| the flip-flop circuit 80 is actuated to cut oil the recording apparatus and when the impression made by coil 3'! passes beneath coil ii the fiip-fiop circuit 80 is restored to its original condition to permit the recording apparatus to become again effective. Similarly, when the impressions made by coils 31 and 31' pass beneath coil 92 the flip-flop circuit 80' is actuated first in one direction and then in the other to render the recording apparatus controlled by it ineffective and efl'ective respectively.

The position 01' coils 9| and 82 with respect to coil 31 corresponds to the position of coils 2|! and 2| with respect to the joint trip contacts II, and this distance may be adjusted by any suitable adjusting means such as that shown diagrammatically at 93, 94, 95 corresponding to the diagrammatic adjustment shown at l5, 16, I1. Additional coils similar to 9|, 92 may be provided for the additional detector coils such as 22. The adjustment 93, 94, 95 may be common to all of the series of coils Si, 92, etc., corresponding to coils 20, 2|, etc., because the relative positions of coils il, 92, etc., are fixed in the same manner as the relative positions of coils 20, 2 I, etc.

The specific crcuit whereby a single coil such as 9i can control the flip-flop circuit III to actuate it first in one direction then in the other in response to two spaced impulses on the tape 42 placed thereon by coils 31 and I1 is disclosed in Fig. 7. Assume the left-hand tube 85 is conducting. A negative pulse from coil 9| in response to the impulse impressed by coil 31 is applied to the grids of both tubes 85 and 81 through anodegrid coupling capacitors and lowers the grid voltage of tube 85 to a point below cut-oil. The grid of tube 8! is already below cut-oi! so this tube is not affected. Tube 85 is quenched. The anode voltage of tube 85 rises. Th s rise is translated in the circuit to a rise in grid voltage of the tube 81 to a point above cut-off voltage, allowing tube 81 to conduct. In conducting, anode voltage of tube 81 drops. This drop in voltage is used to desensitize amplifier tube 51 by lowering the screen voltage. When the impulse impressed by coil 31' passes beneath coil 9i the foregoing action is reversed because the tube 81 is now the conducting tube and there results a rise in anode voltage of tube 81 which again sensitizes amplifier tube 51 by raising the screen voltage.

Having descr'bed our invention, what we claim and desire to secure by Letters Patent is:

1. In a rail fiaw detector car having driving means adapted to move the car over rails connected by joints, said car having means for energizing the rail with fiux, means responsive to variations in said flux caused by defects in the rail, indicating means actuated by said fiux responsive means, said responsive means responding also to variations in flux caused by the joint, means responsive to the rail joint and positioned in advance of said fiux responsive means, a magnetizable member, means for driving said member by said car driving means, means whereby said second rail joint responsive means generates an electrical pulse in response to the joint, impressor means adapted to be energized by said pulse to magnetize said member, a receiver for picking up the magnetization of said member caused by the pulse, and means whereby the output of the receiver in response to the magnetization of the member by said pulse renders the indicating means ineffective.

2. A device as specified in claim 1, characterized by the fact that said receiver is spaced from said impressor in the direction of movement 01 the magnetzable member a distance corresponding to the distance of said flux responsive means from the region of flux affected by the joint when said pulse is generated.

3. A device as specified in claim 1, characterized by a second receiver spaced from the first receiver in the direction of movement of the magnetizable member, and means whereby the output of the second rece'ver in response to the magnetization of the member by said pulse renders the indicating means again effective after the car has traveled a predetermined distance.

4. A device as specified in claim 1, characterized by the fact that said receiver is spaced from said impressor in the direction of movement of the magnetizable member a distance corresponding to the distance of said flux responsive means from the region of fiux affected by the joint when said pulse is generated, a second receiver spaced from the first receiver in the direction of movement of the member, and means whereby the output of the second receiver in response to the magnetization of the member by said pulse renders the indicating means again effective after the car has traveled a predetermined distance.

5. In a rail flaw detector car having driving means adapted to move the car over rails connected by joints, said car having means for energizing the rail with flux, means responsive to variations in said flux caused by defects in the rail, indicating means actuated by said flux responsive means, said responsive means responding also to variations in flux caused by the joint, means responsive to the rail joint and positioned in advance of said fiux responsive means, a magnetizable member, means for driving said member by said car driving means, means whereby said secand rail joint responsive means generates an electrical pulse in response to the joint, impressor means whereby said pulse magnetizes said member, a receiver including a pick-up adapted to be energized by the magnetization of said member to generate a pulse, said indicating means including an electronic amplifier, and means whereby the output of the receiver in response to the magnetization of the member by the pulse gen- :rates a voltage to render the amplifier ineffec- 6. A device as specified in claim 5, characterized by the fact that said receiver is spaced from said impressor in the direction of movement of the magnetizable member a distance corresponding to the distance of said flux responsive means from the region of flux affected by the joint when said pulse is generated,

7. A device as specified in claim 5', characterized by a second receiver spaced from the first receiver in the direction of movement of the magnetizable member, and means whereby the output of the second receiver in response to the magnetization of the member by the pulse generates a voltage to render the amplifier again eil'ective.

8. A device as specified in claim 5, characterized by the fact that said receiver is spaced from said impressor in the direction of movement of the magnetlzable member a distance corresponding to the distance of said flux responsive means from the region of flux affected by the Joint when said pulse is generated, a second receiver spaced from the first receiver in the direction of movement of the member, and means whereby the output of the second receiver in response to the magnetization of the member by the pulse generates a voltage to render the amplifier again effective.

9. In a rail ilaw detector car having driving means adapted to move the car over rails connected by joints, said car having means for energizing the rail with .fiux, means responsive to variations in said flux caused by defects in the rail, indicating means actuated by said flux responsive means, said responsive means responding also to variations iiux caused by the joint, means 1e rail ,ioint and positioned in advance of flux responsive means, a magnetizable member, means for driving said member by said car driving means, means whereby said secand rail joint responsive means generates an electrical pulse in response to the joint, impressor means where? said pulse magnetizes said member, a. receiver picking up the magnetization of said member caused by the pulse, said indicating means including an electronic amplifier, flip-flop circuit for controlling said amplifier to render it effective and ineffective, and means whereby the output of the receiver in response the magnetization of the member by the pulse generates a voltage to energize said flip-flop circult to apply a paralyzing voltage to said ampliziier to render ineffective.

10. A device is specified in claim 9, characteri' ed by the fact that said receiver is spaced from said impressor in the direction of movement of g magnetizable member a distance correspondto the distance of said flux responsive means from the region of flux affected by the joint when said pulse is generated.

153,. device as specified in claim 9, characterri by a second receiver spaced from the first redirection of movement of the magumber, and means whereby the outreceiver in response to the mag- .ember by the pulse generates .rgize the flip-flop circuit and her again effective.

12. A dev at said receiver is spaced from said impress. i r the magnetizable member a distance corresponding to the distance of said flux responsive means from the region of flux affected by the Joint when said pulse is generated, a second receiver spaced from the first receiver in the direction of movement of the member, and means whereby the output of the second receiver in response to the magnetization of the member by the pulse generates a voltage to tie-energize the flip-flop circuit and render the amplifier again efifective.

13. In a rail flaw detector car having drivin means adapted to move the car over rails connected by joints, said car having means for energizing the raii with flux, means responsive to specified in claim 9, character i0 variations in said flux caused by defects in the rail, indicating means actuated by said i'iux responsive means, said responsive means responding also to variations in flux caused by the Joint, means responsive to the rail joint and positioned in advance of said flux responsive means, a magnetizable member means for driving said membar by said car driving means, means whereby said second rail Joint responsive means generates an electrical pulse in response to the Joint, a plurality of impressor means adapted to be energized simultaneously by said pulse to impress a plurality 0t magnetizations on said member, said impressor means being spaced in the direction of movement of said member, the space between impressor means corresponding to the length of the region of flux afl'ected by a joint, 9. receiver for successively picking up the magnetizations of the member, means whereby the output of the receiver in response to the first magnetization renders the indicating means inefiective, and means whereby the output of the receiver in response to the second magnetization renders the receiver again effective.

14. In a rail .fiaw detector car having driving means adapted to move the car over rails connected by joints, said car having means for energizing the rail with flux, means responsive to variations in said ilux caused by defects in the rail, indicating means actuated by said flux responsive means, said responsive means responding also to variations in flux caused by the Joint, means responsive to the rail joint and positioned in advance of said flux responsive means, a magnetizable member, means for driving said memher by said car driving means, means whereby said second rail joint responsive means generates an electrical pulse in response to the joint, a plurality of impressor means adapted to be energized simultaneously by said pulse to impress a plurality of magnetizations on said member, said impressor means being spaced in the direction of movement of said member, the space between im-- said last-named direction renders the indicating means again effective.

15. In a rail flaw detector car having drlvng means adapted to move the car over rails connected by Joints, said car having means for energizing the rail with flux, means responsive to variatons in said flux caused bv defects in the rail, indicating means actuated by said flux responsive means, said responsive means responding also to variations in flux caused by the ioint, means responsive to the rail joint and positioned in advance of said flux responsive means, a magnetizable member in the form of an endless circuit, means for driving said member by said car driving means, means whersby said second rail Joint responsiie means generates an electrical pulse in response to the joint, imoressor means adapted to be energized by said pulse to magnetize said member, flux erasing means positioned in advance of the impressor means, a rea 11 ceiver for picking up the magnetization of said member caused by the pulse, and means whereby the output ofthe receiver in response to the.

magnetization of the member by said pulse renders the indicating means ineffective.

16. In a rail flaw detector car having driving means adapted to move the car over rails connected by Joints, said car having means for ener vgizing the rail with flux, means responsive to an electrical pulse in response to the Joint, im-

pressor means adapted to be energized by said pulse to magnetize said member, a receiver for picking up the magnetization of said member caused by the pulse, means whereby the output of the receiver in response to the magnetization oi the member by said pulse renders the indicating means ineffective, said receiver being spaced from said impressor in the direction of movement of the magnetizable member a distance corresponding to the distance of said flux responsive means from the region of flux afiected by the joint when said pulse is generated, a second receiver spaced from the first receiver in the direction 01' movement of the member, means whereby the output of the second receiver in response to the magnetization of the member by said pulse renders the indicating means again effective after the car has traveled a predetermined distance, said member being in the form of an endless circuit, and flux erasing means positioned in advance of the impressor means.

17. In a rail flaw detector car having driving means adapted to move the car over rails connected by Joints, said car having means for energizing the rail with flux, means responsive to variations in said flux caused by defects in the rail, indicating means actuated by said flux responsive means, said responsive means responding also to variations in flux caused by the joint, means responsive to the rail joint and positioned in advance of said flux responsive means, a magnetizable member, means for driving said member by said car driving means, means whereby said second rail joint responsive means generates an electrical pulse in response to the joint, impressor means whereby said pulse magnetizes said member, a receiver including a pick-up adapted to be energized by the magnetization of said member to generate a pulse, said receiver including a gas discharge tube adapted to be tripped by the pulse generated by the pick-up, said indicating means including an electronic ampliiler, and means whereby the tripping of the gas discharge tube renders the indicator amplifier inefi'ective.

18. In a rail flow detector car having driving means adapted to move the car over rails connected by Joints, said car having means for energizing the rail with flux, means responsive to variations in said flux caused by defects in the rail, indicating means actuated by said flux responsive means, said responsive means responding also to variations in flux caused by the joint, means responsive to the rail joint and positioned in advance of said flux responsive means, a magnetizable member, means for driving said member by said car driving. means, means whereby said second rail Joint responsive means generates an electrical pulse in response to the Joint, impressor means whereby said pulse magnetizes said member, a receiver including a pick-up adapted to be energized by the magnetization of said member to generate a pulse, said receiver including a gas discharge tube adapted to be tripped by the pulse generated by the pick-up, said indicating means including an electronic amplifier, and means whereby the tripping of the gas discharge tube renders the final amplifying stage of the indicator amplifier inefiective.

19. In a rail flaw detector car having driving means adapted to move the car over rails connected by Joints, said car having means for energizing the rail with flux. means responsive to variations insaid flux caused by defects in the rail, indicating means actuated by said fiux responsive means, said responsive means respond- .ing also to variations in flux caused by the joint,

means responsive to the rail Joint and positioned in advance of said flux responsive means, a magnetizable member, means for driving said member by said car driving means, means whereby said second rail joint responsive means generates an electrical pulse in response to the joint, impressor means whereby said pulse magnetizes said member, a receiver including a pick-up adapted to be energized by the magnetization of said member to generate a pulse, said receiver including a gas discharge tube adapted to be tripped by the pulse generated by the pick-up, said indicating means including an electronic amplifier, means whereby, the tripping of the gas discharge tube renders the indicator amplifier ineflective, a second receiver including a pick-up spaced from the first pick-up in the direction of movement of the magnetizable member a distance corresponding to the length of the region of flux afiected by the joint, said second receiver including a gas discharge tube adapted to be tripped by the pulse generated by the second pick-up, and means whereby tripping of the second gas discharge tube renders the indicator amplifier again effective.

20. In a rail flaw detector car having driving means adapted to move the car over rails connected by joints, said car having means for energizing the rail with flux, means responsive to variations in said flux caused by defects in the rail, indicating means actuated by said fiux responsive means, said responsive means responding also to variations in flux caused by the joint, means responsive to the rail joint and positioned in advance of said flux responsive means, a magnetizable member, means for driving said member by said car driving means, means whereby said second rail joint responsive means generates an electrical pulse in response to the joint, impressor means whereby said pulse magnetizes said member, a receiver including a pick-up adapted to be energized by the magnetization of said member to generate a pulse, said receiver including a gas discharge tube adapted to be tripped by the pulse generated by the pick-up, said indicating means including an electronic amplifier, means whereby the tripping of the gas discharge tube renders the indicator amplifier ineflective, a second receiver including a pick-up spaced from the first pick-up in the direction oi movement of the magnetizable member a distance corresponding to the length of the region of flux affected by the joint, said second receiver including a gas discharge tube adapted to be tripped 13 by the pulse generated by the second pick-up, and means whereby tripping of the second gas discharge tube renders the final amplifying stage of the indicator amplifier again effective.

21. In a rail flaw detector car having driving means adapted to move the car over rails connected by Joints, said car having means for energizing the rail with flux, means responsive to variations in said flux caused by defects in the rail, indicating means actuated by said flux responsive means, said responsive means responding also to variations in flux caused by the joint, means responsive to the rail joint and positioned in advance of said fiux responsive means, a magnetizable member, means for driving said member by said car driving means, means whereby said second rail joint responsive means generates an electrical pulse in response to the joint, impressor means whereby said pulse magnetizes said member, a receiver including a pick-up adapted to be energized by the magnetization of said member to generate a pulse, said receiver including a gas discharge tube adapted to be tripped by the pulse generated by the pick-up, said indicating means including an electronic amplifier, means whereby the tripping oi the gas discharge tube renders the indicator amplifier ineflective, a second receiver including a pick-up spaced from the first pick-up in the direction of movement of the magnetizable member a distance corresponding to the length of the region of flux affected by the joint, said second receiver including a gas discharge tube adapted to be tripped by the pulse generated by the second pick-up, means whereby tripping of the second gas discharge tube renders the indicator amplifier again effective, a reset mechanism for the first gas discharge tube, and means whereby discharge of the second gas discharge tube renders said reset mechanism effective.

HARCOURT C. DRAKE.

WALDEMAR I. BENDZ.

WILLIAM E. MESH.

REFERENCES CITED The following references are of record in the file of this patentg UNITED STATES PATENTS Number Name Date 2,113,785 Drake et a1. Apr. 12, 1938 2,481,858 Mesh Sept. 13, 1949 

